The most commonly used route for systemically delivering therapeutically active compounds is the oral route. The most popular method of oral administration is by tablets. Generally, tablets are inexpensive and easy to make. For example, tablets can be made by tightly compressing an amount of a solid therapeutically active compound. However, most tablets contain other ingredients besides the therapeutically active compound. For example, a tablet may also include inactive fillers, binders, diluents, lubricants, disintegrants, coloring agents and flavoring agents.
A tablet is formulated so that any additional ingredients will not detrimentally interact with the therapeutically active compound and so that the therapeutically active compound is delivered systemically. For example, the hardness of the tablet can affect the dissolution rate of the tablet in vivo. While a tablet that is too hard will not easily dissolve, a tablet must be hard enough to withstand the forces of the manufacturing and the distribution processes.
In formulating a tablet, the patient is also considered and thus, often the tablet may contain a coloring agent, which makes the color of the tablet more pleasing to the patent. Similarly, a flavoring agent may be added to make the tablet more palatable.
Sometimes inert fillers are used to obtain the precise size and shape of the tablet desired. The filler is usually selected from a group of compounds that are inert with respect to the therapeutically active compound and that are suitable for consumption by the patient.
The most common method of making a tablet involves mixing the ingredients of the tablet and compressing the mixture in a mold to give it the desired shape and hardness. The mixture of ingredients is usually mechanically compressed by a machine. The compressed mixture may be either wet or dry. However, in a method where the mixture is wet, the mixture or tablet must be dried.
Lubricants can be added to the composition that is to be formed into a tablet to help reduce the frictional wear of the die and its associated parts. Binders may also be added to help promote the adhesion of the different ingredients of the mixture. Disintegrants help the tablet to disintegrate in vivo and thus help to deliver the therapeutically active compound contained in the tablet.
It is also sometimes desirable to coat the tablet. The coating may, for example, be a thin film of light-sensitive material to prevent decomposition of the tablet. Or, the film may have other purposes such as to mask a tablet's unpleasant taste or to delay the disintegration or dissolution of a tablet. A delay may be important, for some therapeutically active compounds irritate the stomach, and it may be desirable to delay the dissolution of the tablet containing such a compound until the tablet reaches the intestine.
Oils have been employed in tablets up to 5% by weight relative to the tablet. For example, vegetable oils have been used as lubricants in concentrations of 1% to 5% by weight relative to the tablet. It has also been noted that vegetable oils may prolong disintegration time of a tablet. Introductory Medicinal Chemistry, J. B. Taylor and P. D. Kennewell, Halsted Press--A Division of John Wiley & Sons, 1981, pp. 37-42. Some tablet compositions have included hydrogenated castor oils and/or hydrogenated cottonseed oils. However, both hydrogenated castor oil and hydrogenated cottonseed oil are solid at room temperature.